ABSTRACT Childhood apraxia of speech (CAS) is a pediatric motor speech disorder that impairs the planning and coordination of movement sequences required to produce understandable speech, affecting 40,000 to 400,000 children in the US. Children with CAS typically make slow progress in therapy and require treatment exceeding the intensity and duration prescribed for other speech disorders. Due to the potential adverse academic, social- emotional, and vocational consequences of communication disorders, effective and efficient treatment is critical for children with CAS. To date, investigations have focused solely on the impact of treatment-level factors (e.g., practice schedule, frequency of feedback, target complexity) on treatment outcome. However, these primarily single-case investigations have not fully accounted for the variability seen in treatment outcomes. Individual-level factors (e.g., initial severity, error consistency, perceptual ability) are frequently hypothesized to be key differentiators in treatment response, but there have been no systematic investigations of these factors. Guided by theoretical understanding about the nature of CAS and supported by empirical and clinical findings, we have identified four individual-level baseline factors which may facilitate or impede response to treatment for CAS: (1) severity in terms of number of errors, (2) severity in terms of consistency of errors, (3) perceptual ability, and (4) intelligibility. We will examine 40 children who previously participated in or are currently participating in treatment for CAS (funded by R01 DC017768; PI: Maas; ClinicalTrials.gov ID NCT03903120), and examine the relationship between the identified person-level factors and response to treatment as captured by changes in speech accuracy. Results will elucidate possible CAS profiles and lay the groundwork for development and implementation of maximally efficient targeted treatments for CAS. This study will contribute critical insight into the impact of initial individual-level factors on treatment outcome, using data from the largest randomized control trial for CAS treatment to date. This proposal fits with NIDCD's Strategic Plan in that it aims to identify factors which contribute to success in treatment for an explicitly noted understudied population (CAS). The long term goal of this research program is to maximize outcomes and communicative quality of life for the many children with CAS and their families.